There has been a concerted effort to develop alloys which will withstand the increasingly more severe conditions required by modern technology. To be of practical utility in many applications, it is also necessary to be able to weld the alloy. Among the high temperature alloys proposed is an iron-chromium-aluminum dispersion-strengthened alloy system, described in detail in U.S. Pat. No. 3,837,930 and No. 3,990,161, which has high temperature strength, good room temperature ductility even after exposure to high temperatures, and exhibits grain stability at elevated temperatures. In general, alloys of the system are composed (by weight) of about 10-40% Cr, about 1-10% Al, up to 10% Ni, up to 10% Co, up to 5% Ti, up to 2% each of rare earth metal, yttrium, zirconium, niobium, hafnium, tantalum, silicon and vanadium, up to 6% each tungsten and molybdenum, up to 0.4% carbon, up to 0.4% manganese and the balance essentially iron, and they include a refractory dispersoid which may range from very small amounts, e.g. (by volume) about 0.1% or less up to about 10% or more. It has been found, however, that when certain alloys in this system are subjected to fusion welding, the dispersoid tends to ripen or agglomerate, and the grain boundaries tend to form transverse to the original microstructure. Such alloys tend to lose high temperature strength at the welds.
Heretofore, it was considered advantageous to incorporate small amounts of titanium, e.g. about 0.5%, in the alloys in order to prevent brittleness that nitrogen in the alloy might cause. Nirtogen is often picked up in preparing the alloy powder. Titanium-containing alloys have been made which have good tensile strength and stress rupture properties at temperatures as high as 1093.degree. C. (2000.degree. F.). However, these alloys tend to lose strength at the welds and this precludes the advantageous use of the alloys in various high temperature applications for which they might otherwise be used.
It has now been found that titanium, which is beneficial in other ways in the iron-chromium-aluminum dispersion strengthened alloys, offers no special advantage in such alloys when they are subjected to fusion welding.
It is the object of the present invention to provide a weldable iron-base dispersion strengthened alloy. A further object is to provide a weldable iron-chromium-aluminum dispersion strengthened alloy. Another object is to provide an alloy with superior weldability for high temperature e.g. 1093.degree. C. (2000.degree. F.) applications. The invention also contemplates providing a welded structure made of an iron-chromium-aluminum dispersion strengthened alloy, which structure is characterized by sound, high strength, and autogeneous weld deposits.
Other objects and advantages will be apparent from the drawings and description which follow.